Brain damage can cause many types of dysfunction. Such dysfunction ranges from complete loss of consciousness (as occurs in a coma), to disorientation and an inability to pay attention (as occurs in delirium), to impairment of one or several of the many specific functions that contribute to conscious experience.
Infections of the brain can be caused by viruses, bacteria, fungi, or, occasionally, protozoa or parasites. Another group of brain disorders, called spongiform encephalopathies, are caused by abnormal proteins called prions.
Twelve pairs of nerves—the cranial nerves—lead directly from the brain to various parts of the head, neck, and trunk. Some of the cranial nerves are involved in the special senses (such as seeing, hearing, and taste), and others control muscles in the face or regulate glands. The nerves are named and numbered (according to their location, from the front of the brain to the back).
Every body movement, from raising a hand to smiling, involves a complex interaction between the central nervous system (brain and spinal cord), nerves, and muscles. Damage to or malfunction of any of these components may result in a movement disorder.
Most nerve fibers inside and outside the brain are wrapped with many layers of tissue composed of a fat (lipoprotein) called myelin. These layers form the myelin sheath. Much like the insulation around an electrical wire, the myelin sheath enables nerve signals (electrical impulses) to be conducted along the nerve fiber with speed and accuracy. When the myelin sheath is damaged, nerves do not conduct electrical impulses normally. Sometimes the nerve fibers are also damaged.
Prion diseases are rare progressive, fatal, and currently untreatable degenerative disorders of the brain (and rarely of other organs) that result when a protein changes into an abnormal form called prion.
Sleep is necessary for survival and good health, but why sleep is needed and exactly how it benefits people are not fully understood. One of sleep's benefits is its restorative effect on people's ability to function normally during the daytime.
Spinal cord disorders can cause permanent severe problems, such as paralysis or impaired bladder and bowel control (urinary incontinence and fecal incontinence). Sometimes these problems can be avoided or minimized if evaluation and treatment are done quickly.
A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction) and symptoms that occur suddenly.
A tumor is an abnormal growth, whether noncancerous (benign) or cancerous (malignant). In many parts of the body, a noncancerous tumor causes few or no problems. However, if any growth or mass in the brain (brain tumor) or spinal cord (spinal cord tumor) is getting larger, it can cause considerable damage because the structures that contain the brain (the skull) and spinal cord (the spine) cannot expand to make room for any increase in their contents.